1. Field of the Invention
The present invention relates to a die for bending a panel edge portion such as for motor vehicles and, specifically, to a press working die assembly configured to be used for negative angle formation and to form a complex shape with a rotating body.
2. Prior Art
In the prior art, in the structure of a die assembly for forming portions having negative angles in a forming method using a press die assembly, for example, as shown in FIGS. 10A and 10B, a rotating body 4c is set to a lower die holder 10 body with an air cylinder 6 or the like. A pad 2 having a pressure source, which serves as a holder of a workpiece set in an upper die holder holds the rotating body 4c and a fixed punch 5. Then, a machining cam 3 moves forward and an edge portion of the workpiece is machined. In addition to a configuration in which the substantially L-shaped rotating body 4c rotationally moves about a point “a” as shown in FIGS. 10A and 10B as described above, there is a known structure in which a column-shaped rotary cam 4d rotates as shown in FIG. 11 (see JP-A-2002-263752, JP-A-2002-263753).
However, in press working die assemblies 1a and 1b in the prior art, since a pressure with which the pad 2 presses down is as large as several tens of ton, the structural strength against a force in the direction of rotation thereof is weak. Therefore, the rotation of the rotating body 4c is prevented by causing the machining cam 3 to hold before the contact of the pad 2. Even with this structure, the machining cam 3 cannot compete with the force of the pad 2. Therefore, it is structurally difficult for the press working die assemblies 1a and 1b to manufacture high quality products.
Therefore, as shown in FIG. 12A, a slide plate 4e is provided in front of the rotating body 4c, and a slide block 14 and the air cylinders 6 for activating the slide block 14 are provided below the slide plate 4e. There is an improved structure in which the rotating body 4c is rotated while pressing an angle R portion of the slide plate 4e against a tapered portion at a distal end of the slide block 14 to set the rotating body 4c, and then the slide block 14 is caused to make a stroke toward the front.
In this structure, the force of the pad 2 can be received by the rotating body 4c. In addition, the thrust generated during the manufacture is also received, so that the quality of the product is improved. However, in this structure, setting of the rotating body 4c is achieved by the air cylinder 6, but the rotating body 4c cannot be restored to its original position. Therefore, as shown in FIG. 12B, a method of lifting the rotating body 4c by a slide pin 15 formed by assembling a spring and a roller bearing is employed for restoring the rotated rotating body 4c to its original position. However, this method has problems to be solved as described below.
1) Since the rotating body has to be held with pressurization of the spring, setting of the strength of the spring is difficult, and if the spring is too strong, the slide block can hardly be placed.
2) The cost is inevitably increased, and an installation space is also needed.
3) Determination of whether the rotating body is rotated with absolute certainty or not can hardly be assessed in the stage of designing.
4) When a drive unit (e.g., air cylinder) for restoring the rotating body to its original position is provided separately, the number of components is increased.